Radiation therapy involves medical procedures that selectively expose certain areas of a human body, such as cancerous tumors, to high doses of radiation. Radiation may also be used to obtain images of the patient during an imaging procedure.
In a radiation treatment procedure, before radiation is delivered, the patient is first setup at the treatment machine. Currently, image guidance is used to correctly setup the patient at the treatment machine, with respect to the planned position. In one technique, one or multiple x-ray projection images of the patient are acquired and registered to a two-dimensional digitally reconstructed radiographs (DRR), calculated for the corresponding x-ray projection direction and geometry using the diagnostic computer tomography (CT) three-dimensional image. The result of this rigid registration is then used to calculate a couch position correction. The couch position correction is then used to adjust the patient position until the patient position matches the planned position In some cases, instead of using two-dimensional image projections for the patient setup procedure, a CT image of the patient may be acquired, and a three-dimensional rigid registration to the planning CT image may be performed.